1. Field of the Invention
The present invention relates to control of xerographic printers and, more particularly, for diagnostic and closed loop process control of xerographic printers.
2. Brief Description of Related Developments
Xerographic printers, such as copiers or laser printers, use an electrostatic voltmeter as a powerful tool for monitoring system and component performance. Voltage measurements obtained with an electrostatic voltmeter can be used to evaluate system performance and diagnose system and subsystem failures. Electrostatic voltmeters are also used for closed loop system and subsystem control.
Electrostatic voltmeters are useful but add cost and complexity to xerographic printers. While the inclusion of electrostatic voltmeters in all xerographic printers would allow for improved printer performance and improved maintenance, the additional unit manufacturing cost and the reduction in available space around the photoreceptor precludes the use of electrostatic voltmeters in low and medium volume xerographic printers.
The disclosed embodiments are directed to a system for controlling a xerographic printer. In one embodiment the system includes a subsystem for carrying out a function of the xerographic printer and affecting an electric field generated by a component. The system further includes a bias transfer roll operated in a constant current mode. A voltage evaluator is coupled to the biased transfer roll for measuring a change in a level of voltage of the bias transfer roll as the component affected by the subsystem passes through a nip region near the bias transfer roll. This change in the voltage level determines operability of the subsystem. Further embodiments are directed to a method for controlling a xerographic printer. In one embodiment the method includes the step of maintaining a biased transfer roll in a constant current mode. The method further includes measuring a change in a level of voltage of the bias transfer roll as a component affected by a subsystem passes through a nip region near the bias transfer roll. This change in the voltage level determines operability of the subsystem.